Method and apparatus for reporting channel state information

ABSTRACT

An indication can be received at a device from a network. The indication can request the device to feedback channel state information corresponding to a first transmit time interval length operation and/or a second transmit time interval length operation. When the indication requests channel state information feedback for the first transmit time interval length operation: a first reference transmit time interval of a first transmit time interval length can be determined based on the transmit time interval in which the indication is received; and a channel measurement to compute the channel state information can be derived using reference signals associated with the first reference transmit time interval, and/or an interference measurement to compute the channel state information can be derived using measurements made on resource elements associated with the first reference transmit time interval. When the indication requests channel state information feedback for the second transmit time interval length operation: a second reference transmit time interval of a second transmit time interval length can be determined based on the transmit time interval in which the indication is received; and a channel measurement to compute the channel state information can be derived using reference signals associated with the second reference transmit time interval, and/or an interference measurement to compute the channel state information can be derived using measurements made on resource elements associated with the second reference transmit time interval.

BACKGROUND 1. Field

The present disclosure is directed to a method and apparatus forreporting channel state information.

2. Introduction

Presently, wireless communication devices, such as user equipmentcommunicate with other communication devices using wireless signals. Incurrent Third Generation Partnership Project Long Term Evolution (3GPPLTE) systems, time-frequency resources are divided into 1 ms subframeswhere each 1 ms subframe includes two 0.5 ms slots and each slot withnormal Cyclic Prefix (CP) duration comprises 7 Single Carrier FrequencyDivision Multiple Access (SC-FDMA) symbols in the time domain in Uplink(UL) and 7 Orthogonal Frequency Division Multiplexed (OFDM) symbols inthe time domain in Downlink (DL). In the frequency domain, resourceswithin a slot are divided into Physical Resource Blocks (PRBs), whereeach PRB spans 12 contiguous subcarriers.

In current LTE systems, resources are usually assigned using a 1 msminimum Transmission Time Interval (TTI) when data is available,referred to as dynamic scheduling. Within each scheduled TTI, in UL, awireless communication device, otherwise known as a User Equipment (UE),transmits data over a Physical Uplink Shared Channel (PUSCH) or aPhysical Sidelink Shared Channel (PSSCH) in PRB-pairs indicated by anuplink/sidelink grant that schedules the data transmission to the UE. InDL, an enhanced NodeB (eNB), such as a base station, transmits data overa Physical Downlink Shared Channel (PDSCH) in PRB-pairs indicated by aDL grant/assignment. The UL/sidelink grant and/or DL assignmentinformation is provided to the UE in a control channel, referred to as aPhysical Downlink Control Channel (PDCCH) or enhanced PDCCH (EPDCCH).The (E)PDCCH channel carries the control information about the databeing transmitted on the current subframe and the information about theresources which UE needs to use for the uplink/sidelink data.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of thedisclosure can be obtained, a description of the disclosure is renderedby reference to specific embodiments thereof which are illustrated inthe appended drawings. These drawings depict only example embodiments ofthe disclosure and do not limit its scope. The drawings may have beensimplified for clarity and are not necessarily drawn to scale.

FIG. 1 is an example block diagram of a system according to a possibleembodiment;

FIG. 2 is an example of subband configuration for CQI reporting in LTEaccording to a possible embodiment;

FIG. 3 is an example illustration of a sTTI and a regular TTI structureaccording to a possible embodiment;

FIG. 4 is an example illustration of multiple-PRB set configuration forsPDCCH monitoring according to a possible embodiment;

FIG. 5 is an example illustration of sPDCCH decoding candidatesbelonging to different PRB-sets according to a possible embodiment;

FIG. 6 is an example illustration of a subframe duration for using ansBW value in deriving sCQI and using the sCQI to schedule sPDSCH in asubframe containing 2-symbol sTTIs according to a possible embodiment;

FIG. 7 is an example illustration of a subframe where the second slot ina TTI does not contain PDCCH symbols according to a possible embodiment;

FIG. 8 is an example illustration of a subband definition update basedon the BW split change between sTTI UEs and non-sTTI UEs according to apossible embodiment;

FIG. 9 is an example illustration of subband definition update andreporting in periodic CQI based on the updated sBW according to apossible embodiment;

FIG. 10 is an example illustration of dropping a report in a reportingoccasion due to a recent sTTI BW change according to a possibleembodiment;

FIG. 11 is an example illustration of a PDCCH command triggeringaperiodic CSI report for both sTTI and regular (1 ms)-TTI according to apossible embodiment;

FIG. 12 is an example flowchart illustrating the operation of a wirelesscommunication device according to a possible embodiment;

FIG. 13 is an example flowchart illustrating the operation of a wirelesscommunication device according to a possible embodiment;

FIG. 14 is an example flowchart illustrating the operation of a wirelesscommunication device according to a possible embodiment;

FIG. 15 is an example flowchart illustrating the operation of a wirelesscommunication device according to a possible embodiment;

FIG. 16 is an example flowchart illustrating the operation of a wirelesscommunication device according to a possible embodiment;

FIG. 17 is an example flowchart illustrating the operation of a wirelesscommunication device according to a possible embodiment; and

FIG. 18 is an example block diagram of an apparatus according to apossible embodiment.

DETAILED DESCRIPTION

According to a possible embodiment, a channel state information requestrequesting a device to feedback channel state information can bereceived. Whether the channel state information request corresponds toregular latency based operation or reduced latency based operation canbe determined. Channel state information can be derived based on a firstreference resource when the channel state information requestcorresponds to regular latency based operation. Channel stateinformation can be derived based on a second reference resource when thechannel state information request corresponds to reduced latency basedoperation. The reduced latency based operation can have a latency lessthan the regular latency based operation. The derived channel stateinformation can be reported to a network.

According to a possible embodiment, an indication can be received at adevice from a network. The indication can request the device to feedbackchannel state information corresponding to a first transmit timeinterval length operation and/or a second transmit time interval lengthoperation. When the indication requests channel state informationfeedback for the first transmit time interval length operation: a firstreference transmit time interval of a first transmit time intervallength can be determined based on the transmit time interval in whichthe indication is received; and a channel measurement to compute thechannel state information can be derived using reference signalsassociated with the first reference transmit time interval, and/or aninterference measurement to compute the channel state information can bederived using measurements made on resource elements associated with thefirst reference transmit time interval. When the indication requestschannel state information feedback for the second transmit time intervallength operation: a second reference transmit time interval of a secondtransmit time interval length can be determined based on the transmittime interval in which the indication is received; and a channelmeasurement to compute the channel state information can be derivedusing reference signals associated with the second reference transmittime interval, and/or an interference measurement to compute the channelstate information can be derived using measurements made on resourceelements associated with the second reference transmit time interval.

According to a possible embodiment, a configuration that configures aplurality of control decoding candidates can be received. A first set ofthe plurality of control decoding candidates associated with a first setof aggregation levels in a first transmit time interval of a subframecan be monitored. A second set of the plurality of control decodingcandidates associated with a second set of aggregation levels in asecond transmit time interval of the subframe can be monitored. Thefirst of the plurality of control decoding candidates and the second setof the plurality of control decoding candidates can be different atleast in one control decoding candidate. The first set of aggregationlevels can be different than the second set of aggregation levels.

According to a possible embodiment, a first set of control decodingcandidates corresponding to a first transmit time interval length in asubframe can be monitored when a device is not configured to communicateusing a second transmit time interval length in the subframe. The secondtransmit time interval length can be shorter than the first transmittime interval length. A second set of control decoding candidatescorresponding to the first transmit time interval length in the subframecan be monitored when the device is configured to communicate using thesecond transmit time interval length in the subframe. The first and thesecond sets can be different. A number of candidates in the second setcan be less than a number of candidates in the first set.

FIG. 1 is an example block diagram of a system 100 according to apossible embodiment. The system 100 can include a wireless communicationdevice 110, such as a User Equipment (UE), a base station 120, and anetwork 130. The wireless communication device 110 can be a wirelessterminal, a portable wireless communication device, a smartphone, acellular telephone, a flip phone, a personal digital assistant, apersonal computer, a selective call receiver, a tablet computer, alaptop computer, or any other device that is capable of sending andreceiving communication signals on a wireless network.

The network 130 can include any type of network that is capable ofsending and receiving wireless communication signals. For example, thenetwork 130 can include a wireless communication network, a cellulartelephone network, a Time Division Multiple Access (TDMA)-based network,a Code Division Multiple Access (CDMA)-based network, an OrthogonalFrequency Division Multiple Access (OFDMA)-based network, a Long TermEvolution (LTE) network, a 3rd Generation Partnership Project(3GPP)-based network, a satellite communications network, a highaltitude platform network, the Internet, and/or other communicationsnetworks. In operation, the wireless communication device 110 cancommunicate with the base station 120 using wireless communicationsignals. These signals can include control and data signals.

Some embodiments can provide a UE procedure for reporting Channel StateInformation (CSI) for reduced latency. In DL cellular communicationsystems, the quality of the signal received by a UE depends on theSignal-to-Interference-and-Noise Ratio (SINR), which can include threeelements: (1) channel quality between a serving cell of a base stationand the UE, (2) the level of interference, such as from other cells, and(3) the noise level. The UE's receiver capability in handling theinterference, such as via interference cancellation, also plays a rolein the signal quality. In DL LTE, the eNB, such as the base station 120,can adapt modulation and coding rate, referred to as Modulation andCoding Scheme (MCS), for a UE based on prediction of the downlinkchannel conditions. A Channel Quality Indicator (CQI) feedback sent bythe UE in the Uplink (UL) is an input to the adaptation. The typicaltime between the UE's measurement of the downlink reference signals andthe subframe containing the correspondingly adapted downlinktransmission on the Physical Downlink Shared Channel (PDSCH) istypically 7-8 ms, which as equivalent to a UE speed of ˜16 km/h at 1.9GHz.

CQI feedback is an indication of the data rate that can be supported bythe channel between the UE and the eNB, taking into account SINR and theUE's receiver capability, such as in handling the interference. For CQI,the UE reports the highest MCS, such as from a set of possible MCSindices, that it can decode with a BLock Error Rate (BLER), computed onthe transport blocks, probability not exceeding 10%. The CQI derivation,such as the BLER calculation can be done based on a CSI referenceresource as follows: A single PDSCH transport block with a combinationof modulation scheme and transport block size corresponding to the CQIindex shown in Tables 1-4, and occupying a group of downlink physicalresource blocks termed the CSI reference resource, can be received witha transport block error probability not exceeding 0.1.

TABLE 1 4-bit CQI Table CQI index modulation code rate × 1024 Efficiency0 out of range 1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4QPSK 308 0.6016 5 QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 816QAM 490 1.9141 9 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 5673.3223 12 64QAM 666 3.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 1564QAM 948 5.5547

TABLE 2 4-bit CQI Table 2 CQI index modulation code rate × 1024Efficiency 0 out of range 1 QPSK 78 0.1523 2 QPSK 193 0.3770 3 QPSK 4490.8770 4 16QAM 378 1.4766 5 16QAM 490 1.9141 6 16QAM 616 2.4063 7 64QAM466 2.7305 8 64QAM 567 3.3223 9 64QAM 666 3.9023 10 64QAM 772 4.5234 1164QAM 873 5.1152 12 256QAM 711 5.5547 13 256QAM 797 6.2266 14 256QAM 8856.9141 15 256QAM 948 7.4063

TABLE 3 Modulation and TBS index table for PDSCH MCS Index I_(MCS)Modulation Order Q_(m) TBS Index I_(TBS) 0 2 0 1 2 1 2 2 2 3 2 3 4 2 4 52 5 6 2 6 7 2 7 8 2 8 9 2 9 10 4 9 11 4 10 12 4 11 13 4 12 14 4 13 15 414 16 4 15 17 6 15 18 6 16 19 6 17 20 6 18 21 6 19 22 6 20 23 6 21 24 622 25 6 23 26 6 24 27 6 25 28 6 26/26A 29 2 reserved 30 4 31 6

TABLE 4 Modulation and TBS index table 2 for PDSCH MCS Index I_(MCS)Modulation Order Q_(m) TBS Index I_(TBS) 0 2 0 1 2 2 2 2 4 3 2 6 4 2 8 54 10 6 4 11 7 4 12 8 4 13 9 4 14 10 4 15 11 6 16 12 6 17 13 6 18 14 6 1915 6 20 16 6 21 17 6 22 18 6 23 19 6 24 20 8 25 21 8 27 22 8 28 23 8 2924 8 30 25 8 31 26 8 32 27 8 33/33A 28 2 reserved 29 4 30 6 31 8

In LTE, the CSI reference resource for a serving cell can be defined asfollows: In the frequency domain, the CSI reference resource can bedefined by the group of downlink physical resource blocks correspondingto the band to which the derived CQI value relates. In the time domain,for a UE configured in transmission mode 1-9 or transmission mode 10with a single configured CSI process for the serving cell, the CSIreference resource can be defined by a single downlink or specialsubframe n-nCQI_ref, assuming CSI report in UL subframe “n”, where forperiodic CSI reporting nCQI_ref is the smallest value greater than orequal to 4, such that it corresponds to a valid downlink or validspecial subframe, where for aperiodic CSI reporting, if the UE is notconfigured with the higher layer parameter csiSubframePatternConfig-r12,nCQI_ref is such that the reference resource can be in the same validdownlink or valid special subframe as the corresponding CSI request inan uplink Downlink Control Information (DCI) format. Other conditionscan also exist in the 3GPP Technical Specification for CQI-ReportConfig.If there is no valid downlink or no valid special subframe for the CSIreference resource in a serving cell, CSI reporting can be omitted forthe serving cell in uplink subframe n. In the layer domain, the CSIreference resource can be defined by any Rank Indicator (RI) andPrecoding Matrix Index (PMI) on which the CQI is conditioned.

In the CSI reference resource, the UE can assume the following for thepurpose of deriving the CQI index, and if also configured, PMI and RI:The first 3 OFDM symbols are occupied by control signaling; No resourceelements used by primary or secondary synchronization signals orPhysical Broadcast Channel (PBCH) or EPDCCH; CP length of thenon-Multicast-Broadcast Single-Frequency Network (MBSFN) subframes;Redundancy Version 0; If CSI Reference Signal (CSI-RS) is used forchannel measurements, the ratio of PDSCH Energy Per Resource Element(EPRE) to CSI-RS EPRE is as given in 3GPP Technical Specification No.36.213, sub clause 7.2.5. The UE can also assume for transmission mode 9CSI reporting: Cell-specific Reference Symbol (CRS) REs are as innon-MBSFN subframes; If the UE is configured for PMI/RI reporting orwithout PMI reporting, the UE-specific reference signal overhead isconsistent with the most recent reported rank if more than one CSI-RSport is configured, and is consistent with rank 1 transmission if onlyone CSI-RS port is configured; Additional assumptions can be made inaccordance with 3GPP Technical Specification (TS) No. 32.213, section7.2.3.

For transmission mode 10 CSI reporting, if a CSI process is configuredwithout PMI/RI reporting: Depending on the number of antenna ports ofthe associated CSI-RS resource, if CRS REs are as in non-MBSFNsubframes, the CRS overhead can be assumed to be the same as the CRSoverhead corresponding to the number of CRS antenna ports of the servingcell; otherwise, the overhead of CRS REs can assume the same number ofantenna ports as that of the associated CSI-RS resource. Additionalassumptions can be made in accordance with 3GPP Technical SpecificationNo. 32.213, section 7.2.3.

For transmission mode 10 CSI reporting, if a CSI process is configuredwith PMI/RI reporting or without PMI reporting: CRS REs can be as innon-MBSFN subframes. The CRS overhead can be assumed to be the same asthe CRS overhead corresponding to the number of CRS antenna ports of theserving cell. Additional assumptions can be made in accordance with 3GPPTechnical Specification No. 32.213, section 7.2.3.

In LTE, A combination of modulation scheme and transport block size cancorrespond to a CQI index if: the combination could be signaled fortransmission on the PDSCH in the CSI reference resource according to therelevant Transport Block Size table, the modulation scheme can beindicated by the CQI index, and the combination of transport block sizeand modulation scheme when applied to the reference resource results inthe effective channel code rate which can be the closest possible to thecode rate indicated by the CQI index. If more than one combination oftransport block size and modulation scheme results in an effectivechannel code rate equally close to the code rate indicated by the CQIindex, only the combination with the smallest of such transport blocksizes may be relevant.

For CSI reporting in LTE, in LTE, there can be two reporting modes inthe time domain: periodic reporting where the UE reports CQI, PMI, andRI with reporting periods configured by the higher layer. PUCCH can beused for this and aperiodic reporting, which can be used to providelarge and more detail reporting in a single reporting instance viaPUSCH. Report Timing can be triggered by DCI.

For subbandCQI feedback, in periodic reporting, The UE can cycle throughdifferent subbands from one reporting instance to the next, to reduceoverhead and the number of bands across the system BW is a configurationparameter. In aperiodic reporting, for higher layer configured subbandreporting, the UE can report the subbandCQI for each band in a singlefeedback report, and for a UE selected subband report, the UE can reportthe subbandCQI for the ‘M’ bands with the highest CQI values.

FIG. 2 is an example of subband configuration 200 for CQI reporting inLTE according to a possible embodiment. The set of subbands (S) a UE canevaluate for CQI reporting can span the entire downlink systembandwidth. A subband is a set of k contiguous PRBs, where k can be afunction of system bandwidth. Note that the last subband in set S mayhave fewer than k contiguous PRBs depending on N_(RB) ^(DL). The numberof subbands for system bandwidth given by N_(RB) ^(DL) can be defined byN=└N_(RB) ^(DL)/k┐ The subbands can be indexed in the order ofincreasing frequency and non-increasing sizes starting at the lowestfrequency.

To reduce latency of communication in LTE, shorter minimum TTI, such asshorter than 1 ms, may be used in UL/DL. Using a shorter minimum TTI(sTTI) can allow the UE to send/receive data using reduced latency whencompared to current LTE systems. In addition, acknowledging each, or agroup containing few, sTTI(s) leading to faster, compared to using 1 msTTI, acknowledging data can help in some applications such asTransmission Control Protocol (TCP) during slow-start phase for users ingood channel conditions. For example, in the TCP slow-start phase for DLcommunication, the network-UE link capacity for a user in good channelcondition can support more data, but the network sends a smaller amountof data because the network is waiting to receive the acknowledgment forthe previously sent data due to the TCP slow-start phase. Therefore,faster acknowledgments, such as from a result of using shorter TTIlength, can enable the network to better utilize the availablenetwork-UE link capacity.

For example, scheduling UE transmission over a sTTI length of 0.5 ms,such as PUSCH scheduled using a PRB spanning a 0.5 ms in a 1 mssubframe, or scheduling UE transmission over a sTTI length of ˜140 us,such as PUSCH scheduled using a shortened PRB spanning 2 SC-FDMA symbolswithin a slot in a subframe, may not only reduce time taken tostart/finish transmitting a data packet, but also can reduce the roundtrip time for possible Hybrid Automatic Repeat reQuest (HARQ)retransmissions related to that data packet.

The PDCCH channel can carry the control information about the data beingtransmitted on the current subframe and the information about theresources which UE need to use for the uplink data. That means it can bemandatory for the UE to decode it successfully if the UE wants to sendsome data or receive something. For reduced latency a shortened PDCCH(sPDCCH) can be defined to play a similar role in a sTTI or a group ofsTTIs. For PDCCH, allocation of resources can happen in terms of ControlChannel Elements (CCEs) which can each be equivalent to 36 REs. One CCEcan be the minimum PDCCH allocation unit.

As the sTTI length becomes smaller, the control overhead can increase,which in turn can increase the complexity and hence the processingdelay, which may negatively impact the latency reduction offered bylow-latency operation. To allow multiplexing of non-sTTI and sTTI it canbe assumed that from eNB perspective, existing non-sTTI and sTTI can beFrequency Division Multiplexed (FDMed) in the same subframe in the samecarrier.

To achieve the potentials of shortened TTI operation, if the CSI reportfor sTTI scheduling can be also provided fast enough to the eNB, betteradaptation to the channel condition can be possible. For example, betteradaptation can include better channel fading, interference information,etc. Faster CSI, as compared to existing CSI reporting mechanisms, canhelp in reducing the latency of data transmission by better schedulingand utilizing the available channel capacity. For sTTI, the reportingperiod, such as the CSI reporting delay or periodic reporting period,can be shrunk. To reduce CSI feedback a larger subband size can be usedfor sTTI.

FIG. 3 is an example illustration of a regular TTI, such as a 1 mssubframe length TTI, and a sTTI structure 300 according to a possibleembodiment. As discussed above, the UE can be expected to look forcontrol signaling that grants resources for either sTTI basedtransmission or a regular TTI based transmission, where regular TTI cansometimes also be referred to as 1 ms TTI. The control signaling itselfmay be received by the UE in a control channel of a sTTI, such as asPDCCH sent in sTTI, or it may be received on a legacy control channel,such as a PDCCH in legacy control region or EPDCCH. If the controlsignaling includes a CSI request, the UE can include CSI information inthe transmission granted by the control channel. How the UE computesincluded CSI information can depend on whether the CSI requestcorresponds to sTTI based operation (sCSI), or whether the CSI requestcorresponds to regular TTI based operation (rCSI).

For example, if the CSI request corresponds to sTTI based operation, theUE can derive the channel measurement to compute the CSI informationusing reference signals associated with the reference sTTI in which theCSI request is received. Similarly, the UE can derive the interferencemeasurement to compute the CSI information using measurements made onresource elements associated with the reference sTTI in which the CSIrequest is received. If the CSI request corresponds to regular TTI basedoperation, the UE can use different reference signals and resourceelements to make its channel and interference measurements. Regular TTIcan typically be a subframe with 14 OFDM symbols and sTTI can be a timeresource within the subframe with shorter duration, such as two (2) OFDMsymbols. Some examples are discussed below using the structure 300.

In one example, if the UE receives a CSI request using a sPDCCH in sTTI1of subframe n, the UE can use reference signals transmitted in the OFDMsymbols corresponding to sTTI0, where sTTI0 can overlap with PDCCH, andsTTI1 of subframe n, and optionally reference signals received inprevious subframes, such as subframe n−1, to derive its channelmeasurements. Here, since the CSI request is transmitted in a sTTI, theUE can implicitly assume that the CSI request is for sTTI basedoperation. In this case, sTTI1 can be considered as the reference sTTI.

In another example, if the UE receives a CSI request using a PDCCH inthe legacy control region of subframe n, and if the PDCCH corresponds tosTTI operation, the UE can use reference signals transmitted in the OFDMsymbols corresponding to sTTI0 of subframe n, or more generally, thesTTIs that overlap with the legacy control region, and optionallyreference signals received in previous subframes, such as subframe n−1,to derive its channel measurements. Here, since the CSI request istransmitted in the legacy control region, the UE can determine whetherthe CSI request is for sTTI based operation or regular TTI basedoperation based on whether the PDCCH corresponds to sTTI operation orregular TTI operation respectively, such as based on using differentRadio Network Temporary Identifier (RNTI) values used in CyclicRedundancy Check (CRC) scrambling of PDCCHs of sTTI and regular TTIoperation. In this case, sTTI0 can be considered as the reference sTTI.

In another example, if the UE receives a CSI request using an EPDCCH insubframe n, and if the EPDCCH corresponds to sTTI operation, the UE canuse reference signals transmitted in the OFDM symbols corresponding to asubset of sTTIs of subframe n, such as, sTTI6 or sTTIs 5 and 6, andoptionally reference signals received in previous subframes, such assubframe n−1, to derive its channel measurements. Here, since the CSIrequest is transmitted in the legacy control region, the UE candetermine whether the CSI request is for sTTI based operation or regularTTI based operation based on whether the EPDCCH corresponds to sTTIoperation or regular TTI operation respectively, such as based usingdifferent RNTI values used in CRC scrambling of PDCCHs of sTTI andregular TTI operation. In this case, sTTI6 can be considered as thereference sTTI.

In another example, if the PDCCH carrying the CSI request corresponds toregular TTI based operation, the UE can use reference signalstransmitted until the end of subframe n, and optionally referencesignals received in previous subframes, such as subframe n−1, to deriveits channel measurements.

In another example, if the UE receives a CSI request using a sPDCCH insTTI of subframe n, and if information decoded from the sPDCCHexplicitly indicates that the CSI request is for regular TTI basedoperation, such as using a bit or code point in the DCI, the UE can usereference signals transmitted until the end of subframe n, andoptionally reference signals received in previous subframes, such assubframe n−1, to derive its channel measurements.

In the above examples, the reference signals used by the UE for derivingthe channel measurements may have different configurations across thesystem bandwidth or sTTIs of a subframe or across different subframes.For instance, CSI-RS for a portion of system bandwidth can belong tosTTI operation and CSI-RS for anther portion can belong to regular TTIoperation. The UE can use CSI-RS signals in both system bandwidthportions for deriving channel measurements in response to the CSIrequest corresponding to the regular TTI-based operation or thesTTI-based operation.

The number of reference signals the UE may use for channel measurementmay be restricted by higher-layer configuration. For example, the UE mayonly use reference signals in reference sTTI or reference signals in thesubframe up to the reference sTTI. This may be the case for CRSreference signals. For CSI-RS reference signals, the UE may only use themost recent reference signals, no later than the reference sTTI.

While the above examples discuss the reference signals that the UE canuse for deriving channel measurements, similar approaches to thosedescribed above can also be used by the UE for determining resourceelements for deriving interference measurements used in the CSIcomputation. The interference measurement may be based on CRS referencesignals or CSI-IM resources.

The CSI information reported by the UE typically includes a CQI index.Typically, the UE derives a highest possible CQI index such that asingle transport block with a combination of modulation scheme andtransport block size corresponding to the CQI index, such as using atable similar to the ones described above, can be received with atransport block error probability not exceeding 0.1. The channel andinterference measurements described above derived by the UE can help theUE to identify the appropriate highest possible CQI index satisfying theabove criterion. For the block error probability computation the UE canassume a CSI reference resource.

If the CSI request corresponds to sTTI based operation, the UE canassume a CSI reference resource corresponding to sTTI operation.Alternately, if the CSI request corresponds to regular TTI basedoperation, the UE can assume a CSI reference resource corresponding toregular TTI operation. Allowing the UE to assume different types of CSIresources for regular and sTTI based operation can improve the accuracyof CSI information transmitted by the UE. For example, if the CSIrequest corresponds to sTTI based operation, the CSI reference resourcecan correspond to a reference sTTI in the time domain, where examples ofreference sTTI are described above, and a set of PRBs within thereference sTTI in the frequency domain. If the CSI request correspondsto regular TTI operation, the CSI reference resource can correspond to areference subframe in the time domain and a set of PRBs within thereference subframe in the frequency domain. The duration of a sTTIcorresponding to a duration of 2 or 7 OFDM symbols can be smaller thanthe duration of a subframe corresponding to a duration of 14 OFDMsymbols. Also, the set of PRBs within the reference sTTI can bedifferent from the PRBs within the reference subframe. More details onCSI reference resource for sTTI based operation as described in latersections below.

The rank of the channel may not change between regular TTI and sTTIoperation. Thus, in some examples, the UE may assume for sTTI CSIcomputation, the rank can be the same as the rank of the most recent RIreported for regular TTI. This may help with reducing the sTTI CSIcomputation complexity. The regular TTI and sTTI CSI configurations maybe in the same CSI process. In some cases, the UE may be explicitlyconfigured with a RI-reference regular TTI CSI process, such as a sTTICSI process, to use for sTTI operation. This may be case when regularTTI and sTTI CSI are independently configured in different CSIprocesses. The set of restricted RIs with precoder codebook subsetrestriction may be same for sTTI and regular TTI CSI. The CSI reportingmode may support RI reporting for regular TTI CSI. In some examples, thewideband CQI for sTTI operation may be encoded differentially, such as 1or 2-bit, with respect to most recent wideband CQI reported for regularTTI operation to help with reducing the feedback overhead. This may beuseful when CSI for both regular TTI and sTTI are reported at the sametime. For example, wideband differential CQI sTTI offset level=sTTIwideband CQI index—regular TTI wideband CQI index with an example 1-bitmapping shown in Table 5 below:

TABLE 5 Mapping wideband differential CQI value to offset level widebanddifferential CQI sTTI offset level Offset level 0 0 1 −1

The UE can monitor PDCCH or sPDCCH candidates which may carry the CSItrigger. The UE can be configured to monitor sPDCCH candidates carryingsDCI, which may trigger the sCSI report, over multiple sets of RBs.

FIG. 4 is an example illustration 400 of multiple-PRB set configurationfor sPDCCH monitoring according to a possible embodiment. In each sTTIof a subframe where the UE is enabled for sTTI operation, the UE canmonitor some or all of the configured PRB-sets. For the example shown inthe illustration 400, the eNB can configure 6 PRB-sets for sPDCCHcontrol monitoring. Subframe n+1 has a legacy PDSCH allocationoverlapping some sPDCCH monitoring sets, such as 4, 5, 6, however, theeNB can use the remaining sets, such as 1, 2, 3, to schedule sPDSCH inthat subframe.

FIG. 5 is an example illustration 500 of sPDCCH decoding candidatesbelonging to different PRB-sets according to a possible embodiment,where different PRB sets are represented by different hashing. Set 3includes some of the decoding candidates belonging to sets 1 and 2. Set6 includes some of the decoding candidates belonging to sets 4 and 5. Toget frequency diversity, in a 2-symbol TTI, CCEs of the first three setscan be mapped within the first half of the system BW, and CCEs of thesecond three sets can be mapped within the second half of the system BW.

Different PRB-sets for sPDCCH monitoring can have different bandwidths,different numbers of decoding candidates, and may support differentAggregation Levels (AL). For instance, as shown in the illustration 500,each of sets 1, 2, 4, 5 from the illustration 400 may include twodecoding candidates with AL=1, and one decoding candidate with AL=2taking about 3 RBs assuming 36 REs/CCE; whereas sets 3 and 6 may haveone candidate with AL=4 and one candidate with AL=8 in addition to theone candidate with AL=1 and one candidate with AL=2, taking about 12RBs.

Among different sTTIs of a subframe, the sets to be monitored in eachsTTI can change with sTTI index within the subframe to provide moreflexible sPDCCH scheduling. For instance, assuming 6 sTTIs with sPDCCHcandidates in a subframe, sets (1,6); (3,4); (2,6); (3,5); (1,6); (3,4);can be monitored in the sTTIs 1, 2, 3, 4, 5, 6 respectively of thesubframe. For instance, sets (1,6) correspond to CCE0, 1, 16-23 and sets(3,4) correspond to CCE0-7, 16, 17. More generally, the UE can beconfigured with multiple sets, such as via higher layer signaling, tomonitor sPDDCH candidates. For each sTTI in which sPDCCH candidates aremonitored, the UE can determine a subset of sets from the multipleconfigured sets based on one or more of the following parameters: UEidentifier, subframe index corresponding to the sTTI, sTTI index, and/orslot index corresponding to the sTTI. The UE can then monitor sPDCCHcandidates belonging to the subset of sets for receiving sPDCCH in thesTTI.

Increasing the number of sPDCCH PRB-sets can increase sPDCCH schedulingflexibility. If a large number of PRB-sets is needed, the eNB may limitthe number of sets to be monitored in a subframe. Even if the UE missesthe eNB indication of set limitation, the UE can monitor a defaultPRB-set to monitor sPDCCH candidates in a subframe. The default set canoverlap with most of the configured PRB-sets to increase the sPDCCHscheduling flexibility. For instance, in the example above, a defaultset can be made of one candidate with each of the aggregation levels 1,2, 4, and 8 belonging to the different PRB-sets. For example, in oddsTTIs of the subframe, the default set can contain 4 sPDCCH decodingcandidates: CCE0 for AL=1, CCE16, 17 for AL=2, CCE0-3 for AL=4, andCCE16-23 for AL=8, and for even sTTIs of the subframe, the default setcan contain CCE16 for AL=1, CCE0, 1 for AL=2, CCE16-19 for AL=4, andCCE0-7 for AL=8.

Assuming 4-6 Blind Decodes (BDs) per sTTI as considered in the examplesgiven above, and considering 6 sTTIs in a subframe with sPDCCH decodingcandidates, such as 2 sTTIs in the first slot and 4 sTTIs in the secondslot, there can be 24-36 additional BDs needed per subframe. Noting thatnot all of the sPDCCH BDs need to be processed at the same time, as theyoccur in different sTTIs of the subframe, the resulting processing delaydue to the additional BDs may be negligible or tolerable. For example,the following assumes 32 PDCCH BDs, such as in the first two OFDMsymbols of a subframe, can be processed by the end of the first slot inthe subframe, and also assumes there is no additional hardware forprocessing the BDs due to the sTTI operation. In that case, if all ofthe sPDCCH decoding candidates would have happened at the sTTIs of thesecond slot, up to 32 of them could have been processed using theunoccupied BD processing unit. However, some of the sPDCCH decodingcandidates belong to the sTTIs of the first slot, such as 8-12 BDs inour examples. For those BDs, since there is no additional hardware, theymay need to wait until the PDCCH decoding candidates are processed. Toavoid additional processing delay for those 8-12 BD candidates, thenumber of PDCCH BD candidates can be reduced from 32 to 24 or 20. Ifmore than 20-24 PDCCH BD candidates are needed, the number of sPDCCH BDsin the first slot can be reduced. For example, in the examples givenabove, the UE can monitor only PRB-set 1 in sTTIs of the first slot. Insuch a case, 28 PDCCH BDs, and only 2 BDs per sTTI in the first slot maybe possible.

One step in designing a CSI report can be to define a CSI referenceresource discussed above. Throughout this disclosure, a CSI reported forsTTI operation can be referred to as an sCSI. To define ansCSI-reference resource, some considerations can be made with respect tothe definition of the CSI-reference resource for 1 ms-TTI.

One consideration can be that each 1 ms-TTI, such as regular TTI orsubframe, can comprise multiple sTTIs, which can have differentcharacteristics related to the sCSI reference resource. For example, forslot-level sTTI, such as an sTTI spanning 7 OFDM symbols in a subframe:the first slot in a subframe can contain PDCCH symbols which are notpresent in the second slot sTTI in the subframe. For 2-symbol-sTTIs,such as an sTTI spanning 2 OFDM symbols in a subframe: some of the 2symbol sTTIs in a subframe may not contain CRS REs whereas some of thesTTIs in the subframe may contain CRS REs.

Another consideration can be UE-specific overhead in CSI-referenceresource. Note that in the following design methodology of LTE for TM9for 1 ms-TTI, if the UE is configured for PMI/RI reporting or withoutPMI reporting, the UE-specific reference signal overhead can beconsistent with the most recent reported rank if more than one CSI-RSport is configured, and can be consistent with rank 1 transmission ifonly one CSI-RS port is configured. Also, note that in sTTI and 1-msTTI, UE-specific reference signal REs can be different, such as in termsof location and quantity per sTTI. Additionally, note that to saveUE-specific reference signal overhead for sTTI operation, not all sTTIsmay contain the reference signal. Further, note that sCSI may notinclude sRI, and for rank information, the eNB may rely on the mostrecent RI reported, such as for 1 ms operation, for the purpose of sTTIscheduling, subject to a possible rank restriction, such as where rankshigher than 4 may not be possible in an sTTI, whereas ranks up to 8 canbe possible for a subframe. Also, note that different number of CSI-RSand sCSI-RS ports may be configured for the UE.

Another consideration can be the case of system Bandwidth (BW) splitbetween sTTI UEs and regular 1-ms TTI UEs. In the present disclosure theBW portion given to the sTTI UEs can be referred to as sBW and the BWportion given to the regular UEs can be referred to as rBW. The existingCSI-reference resource can be defined by the group of DL PRBscorresponding to the band to which the derived CQI value relates. InLTE, the UE can select the highest CQI index that satisfies thecondition: A single PDSCH TB with a combination of modulation scheme andTBS corresponding to the CQI index in the CSI reference resource couldbe received with a TB BLER not exceeding 0.1. For sTTI operation, theband to which the derived sCQI value relates can be a function of thesBW. For instance, a wideband sCQI may be derived only over a part ofthe system BW, such as the sBW, at the time of sCQI derivation or thewideband sCQI may be derived only over anaverage/typical/maximum/minimum sBW value.

FIG. 6 is an example illustration of a subframe duration 600 for usingan sBW value in deriving sCQI and using the sCQI to schedule sPDSCH in asubframe containing 2-symbol sTTIs according to a possible embodiment.At the beginning of the subframe, an eNB may trigger an aperiodic sCSIreport. If scheduling timing allows for derivation and reporting, andalso possibly triggering the report, of sCQI in a subframe, andscheduling of an sPDSCH in the same subframe according to the reportedsCQI, the sCQI reference resource can be determined based on the sBWvalue indicated at the beginning of the subframe. Note that if the BWsplit is the same for multiple consecutive subframes, such as twosubframes, the same approach of having the band to which the derivedsCQI value relates as a function of the sBW, can be feasible.

In the sCSI reference resource, the UE can assume the followingimplementations for the purpose of deriving the sCQI index, and if alsoconfigured, sPMI and sRI. According to a first possible approach forslot-level TTI, the first x, such as 2, OFDM symbols of the slot can beoccupied by control signaling. No resource elements may be used byprimary or secondary synchronization signals or PBCH or EPDCCH. Thenon-MBSFN subframes can have CP length. The Redundancy Version can be 0.If CSI-RS is used for channel measurements, the ratio of sPDSCH EnergyPer Resource Element (EPRE) to sCSI-RS EPRE can be as given in TS36.213, sub clause 7.2.5. For transmission mode 9 CSI reporting whereCRS REs are as in non-MBSFN subframes, if the UE is configured forPMI/RI reporting or without PMI reporting, the UE-specific referencesignal overhead can be consistent with the most recent reported rank,subject to a possible maximum rank restriction for sTTI, if more thanone CSI-RS port is configured, and can be consistent with rank 1transmission if only one CSI-RS port is configured. Having x, such as 2,OFDM symbols of the slot in the first approach can account for thesPDCCH as well, if 2 symbol sPDCCH for slot-level used. This designalong with the current 3GPP agreements of legacy PDCCH can be used totransmit sDCI, such as DCI for sPDSCH and/or sPUSCH, and for CRS-basedsPDCCH, sPDCCH may not be mapped to the PDCCH region, since, the firstslot can carry PDCCH and the second slot can carry sPDCCH.

In the first approach, the derived sCQI can be equally applicable forscheduling the first slot and the second slot in a subframe. Analternative to the first approach can be to keep the existing assumptionof the 3 OFDM symbols of PDCCH in LTE for CSI-reference resource, butnow in a slot instead of a subframe. According to a second possibleapproach for slot-level TTI, the first 3 OFDM symbols of the slot can beoccupied by control signaling.

FIG. 7 is an example illustration of a subframe 700 where the secondslot in a TTI does not contain PDCCH symbols according to a possibleembodiment. Based on the sCQI-reference resource definition, an eNB maychoose a higher MCS index corresponding to the reported sCQI index. Forexample, there may not be whole symbols allocated to the sPDCCH region,such as when only some RBs and not the whole BW may be allocated forsPDCCH. In this case, since the second slot in each subframe does nothave any PDCCH symbols, depending on the selected sCSI-referenceresource, such as an assumption on the number of OFDM symbols for PDCCH,the eNB may need to take into account some adjustment with respect toreported CQI, depending on which slot, such as the first slot in thesubframe or the second slot in the subframe, the eNB schedules an sPDSCHtransmission. Another approach can be for the UE to report two sCQItypes: one assuming a certain number, x, of PDCCH symbols in a slot, andanother one assuming no PDCCH symbols in a slot.

As an example, if the sCSI-reference resource assumes 3 OFDM symbols forPDCCH, when eNB schedules the first slot in a subframe based on thereported sCQI, the eNB may choose the corresponding MCS index to thereported sCQI index. When the eNB schedules the second slot in asubframe based on the reported sCQI, the eNB may choose a slightlyhigher MCS index corresponding to the reported sCQI index.Alternatively, the MCS index table may not be changed, but a fixed orsignaled offset can be assumed/indicated by/to the UE if the second slotin the subframe is scheduled.

As another implementation in the sCSI reference resource, the UE canassume the following for the purpose of deriving the sCQI index, and ifalso configured, sPMI and sRI, for 2-symbol-level TTI. No resourceelements may be used by primary or secondary synchronization signals orPBCH or EPDCCH. The non-MBSFN subframes can have CP length. TheRedundancy Version can be 0. If CSI-RS is used for channel measurements,the ratio of sPDSCH EPRE to sCSI-RS EPRE can be as given in 36.213,subclause 7.2.5. For transmission mode 9 CSI reporting, CRS REs can beas in non-MBSFN subframes in a 2-symbol TTI containing CRS REs and ifthe UE is configured for PMI/RI reporting or without PMI reporting, theUE-specific reference signal overhead can be consistent with the mostrecent reported rank, subject to a possible maximum rank restriction forsTTI, if more than one CSI-RS port is configured, and can be consistentwith rank 1 transmission if only one CSI-RS port is configured;

To efficiently utilize the sTTI resources according to the sCQIfeedback(s), in a first approach if the first, and possibly the second,2-symbol TTI(s) in a subframe can include the PDCCH control symbols,then eNB may use a lower MCS index than the one derived from the sCQIreported by the UE based on the above design. If a 2-symbol TTI that theeNB schedules does not contain CRS REs, the eNB may choose a slightlyhigher MCS index or UE may get an MCS that has an offset to be indicatedto the UE or to be assumed by the UE similar to the slot-level designabove.

In a second approach to efficiently utilize the sTTI resources accordingto the sCQI feedback(s), the UE can send two types of sCQI. One sCQI canbe based on an sCSI-reference resource which assumes a certain number,x, such as 2 or 3, of OFDM symbols for PDCCH and another sCQI feedback,such as an offset sCQI to the sCQI derived based on the sCSI-referenceresource. The type, such as the first type only or the first type andthe second type, may also be indicated to the UE, such as via a field in(E)PDCCH or sPDCCH or via higher layers.

If a 2-symbol TTI that the eNB schedules does not contain CRS REs, theeNB may choose a slightly higher MCS index or the UE may get an MCS thathas an offset to be indicated to the UE or to be assumed by the UEsimilar to the slot-level design above. The UE may also send anothersCQI as an offset to the one that assumes certain CRS overhead.

For the case of UE-specific overhead, similar approaches to get sCQIwhen UE-specific RS is absent in an sTTI are possible. For example, sCQIwhen no UE-specific RS is present in an sTTI can be derived based on anoffset with respect to sCQI derived based on the presence of UE-specificRS present and based on a new sCSI reference resource definition. Forexample, basically two different sCQI types can be reported: with andwithout presence of UE-specific RS assumption.

A CSI reference resource can be defined in a valid DL or specialsubframe in LTE. For a UE configured in transmission mode 1-9 ortransmission mode 10 with a single configured CSI process for theserving cell, the sCSI reference resource can be defined by a singledownlink or special sTTI n-nsCQI_ref, assuming sCSI report in UL sTTI“n”, where for periodic sCSI reporting nsCQI_ref can be the smallestvalue greater than or equal to 4, such that it corresponds to a validdownlink or valid special sTTI, and where for aperiodic sCSI reporting,if the UE is not configured with the higher layer parametercsiSubframePatternConfig-r12, nsCQI_ref can be such that the referenceresource is in the same valid downlink or valid special subframe as thecorresponding sCSI request in an uplink DCI format.

The CQI indices and their interpretations for LTE are described abovefor reporting CQI based on different modulations. For sTTI operation,the Turbo-code length can become smaller due to the limited number ofresources in time, such as the limited number of OFDM symbols, and theexisting tables can be reused but with some modifications. Table 6 is anumber of non-CRS REs in a 2-symbol sTTI for 2 CRS antenna ports. A codeblock in LTE can vary from 40 bits in length to 6144 bits. Consideringthe REs available in a subframe assuming 2 CRS antenna ports and 2symbol control, (14−2)*12−16=128 REs/PRB. Whereas in 2-symbol there are20 RE/RB if CRS present and 24 RE/RB if CRS is absent.

TABLE 6 Number of non-CRS REs in a 2-symbol sTTI, (2 CRS antenna ports).#of RBs configured available REs in available REs in a for sTTIoperation a sTTI with CRS sTTI without CRS 6 120 144 15 300 360 25 500600 50 1000 1200 75 1500 1800 100 2000 2400

If a UE is configured to report sCQI corresponding to a sTTI length,such as to get the most update information about the channelcharacteristics, the CQI tables used for regular 1 ms-TTI operation inLTE may be reused subject to some modifications. New tables can be madeas an offset to current CQI/MCS tables. The offset with respect toCQI/MCS table entries can be to compensate the turbo-code loss for thesmaller TTI length. The offset can be tabulated in the specifications asa one-to-one mapping of the CQI/MCS tables. Alternatively, an offset canbe signaled to the UE, such as in the aperiodic CSI trigger or in1-level DCI valid for a subframe or via higher layer signaling.Different CQI/MCS tables can also be made. Subsampling the currentCQI/MCS tables can additionally be used to make new tables.

FIG. 8 is an example illustration 800 of a subband definition updatebased on the BW split change between sTTI UEs and non-sTTI UEs accordingto a possible embodiment. Subband size in frequency units can be updatedbased on the system bandwidth split between sTTI UEs and non-sTTI UEs orbased on the BW given to that sTTI in case multiple sTTI lengths areallowed simultaneously in the system. For sTTI operation with aparticular sTTI length, a subband can be a set of k contiguous PRBs. Thevalue of k can be derived in different ways. For example, a new k, whichcan be different than the k defined for regular TTI, can be defined foreach sTTI length and for a total DL system BW or maximum allowable sTTIBW, which can be defined or configured. The value of k can be fixed inthe specifications for each sTTI length and for a total DL system BW ormaximum allowable sTTI BW. Alternatively, k can be determined via higherlayer signaling such as Radio Resource Control (RRC) or MAC. Forinstance, similar to the existing RRC signaling, a new field in CQIconfiguration, such as CQI-ReportConfig, can be defined. As anotherexample, k for sTTI operation can be a function of BW split between sTTIand non-sTTI UEs. The split can be dynamic, semi-static, or static. Thek for 1 ms TTI operation with a shortened processing time, such as whereminimum timing is reduced compared to that of legacy LTE operation, or 1ms-UEs aware of some sTTI related information can also be determined viaone of the above methods. The first example may provide simplicity ofdesign and specification, but a UE may end up sending a report for afrequency region where it may not be scheduled at all. Some embodimentsbelow can focus on the second example. The second example may be donewhen the BW split is done by higher than physical layer signaling.

FIG. 9 is an example illustration 900 of subband definition update andreporting in periodic CQI based on the updated sBW according to apossible embodiment. The subbands can be defined as shown in theillustration 800. Subbands B4 and B5 may not be part of the updated sTTIBW. In periodic reporting as the sTTI BW changes, only subbandsbelonging to the current BW split may be reported. If it is a subbandturn to be reported, and now the subband does not belong to the set offrequencies in the updated sTTI BW, according to a possible alternative,the UE can cycle through subbands to find a subband belonging to thesBW, such as the sTTI BW, and reports that in that occasion. It is alsopossible that for a certain range of the sBWs, subband definition, suchas a “k” value, can be kept the same.

FIG. 10 is an example illustration 1000 of dropping a report in areporting occasion due to a recent sTTI BW change according to apossible embodiment. According to this possible alternative when it is asubband turn to be reported, and now the subband does not belong to theset of frequencies in the updated sTTI BW, a certain number of periodicreport occasions, which can be one (1) occasion depending on the timedistance from the sTTI BW update, can be dropped to give the UE time tocompute the subband CQIs based on the updated subband definition.

For an aperiodic CQI report, the UE can discard the aperiodic DCItrigger if it cannot update subband reports in a timely fashion.Alternatively, the eNB, after changing the sBW, may not trigger anaperiodic report sooner than x ms/TTI for both a sTTI UE and a regularTTI UE with enhanced capability of sTTI knowledge. If the FDM BW splitchanges faster than higher layer signaling for configuring CQI reportfor aperiodic CQI, the UE can derive the updated subband indices basedon the higher layer configuration of the CQI report and the sBW splitfor aperiodic and periodic reports. As an example, forperiodic/aperiodic report, k=4 and sTTI BW in number of RBs calledN_(RB) ^(DL,s)=20, then the number of possible subbands can be 5. If theupdated N_(RB) ^(DL,s)=10, then the number of subbands can become:10/4=2.5, then there can be 3 subbands. If the updated N_(RB)^(DL,s)=40, number of subbands becomes: 40/4=10, then there can be 10subbands. In this example, subband size for sTTI can change with higherlayer, and can be fixed to 4 RBs. According to another possibleimplementation, if the FDM BW split changes faster than higher layersignaling for configuring CQI report for aperiodic CQI, a new “k” can besignaled via the physical layer or via a higher layer.

The subband CQI can generally be computed as a differential to awideband CQI. The wideband CQI can be calculated based on the BW split.For example, the wideband CQI can be calculated for the entire sBW forthe sTTI. If the BW split changes via a higher layer, then a new “k” canbe signaled via higher layer.

Table 7 is a table of subband size (k) and number of subbands (M) in Svs. downlink system bandwidth in current LTE systems, which can besimilar to table 7.2.1-5 as given in TS 36.213. For an “M” selectedsubband case, there can be a new set of subband size (k) and number ofsubbands (M) in subband set S vs. downlink system bandwidth given tosTTI operation, which can be defined. The sTTI length can be taken intoaccount in determining this table. A regular TTI UE with enhancedcapability of sTTI knowledge may only report subbands belonging to theBW given to non-sTTI UEs. The BW given to sTTI UEs can be signaled tothose UEs as well.

TABLE 7 Subband Size (k) and Number of Subbands (M) in S vs. DownlinkSystem Bandwidth in current LTE systems System Bandwidth N_(RB) ^(DL)Subband Size k (RBs) M 6-7 NA NA  8-10 2 1 11-26 2 3 27-63 3 5  64-110 46

Table 8 is a table of subband size (k) and number of subbands (M) in Svs. downlink system bandwidth allocated to 1 ms-TTI UEs with BW splitknowledge. This table can be for UEs operating with 1 ms TTI but awareof BW split between 1 ms UEs and sTTI UEs.

TABLE 8 Subband Size (k) and Number of Subbands (M) in S vs. DownlinkSystem Bandwidth allocated to 1 ms-TTI UEs with BW split knowledgeSystem Bandwidth allocated to 1 ms-TTI UEs N_(RB) ^(DL) Subband Size k(RBs) M 6-7 NA NA  8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

Table 9 is a table of subband size (k) and number of subbands (M) in Svs. downlink system bandwidth allocated to slot-level TTI UEs.

TABLE 9 Subband Size (k) and Number of Subbands (M) in S vs. DownlinkSystem Bandwidth allocated to slot-level TTI UEs System Bandwidthallocated to 0.5 ms-TTI UEs N_(RB) ^(DL) Subband Size k (RBs) M 6-7 NANA  8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

Table 10 is a table of subband size (k) and number of subbands (M) in Svs. downlink system bandwidth allocated to 2-symbol-TTI UEs.

TABLE 10 Subband Size (k) and Number of Subbands (M) in S vs. DownlinkSystem Bandwidth allocated to 2-symbol-TTI UEs System Bandwidthallocated to 2-symbol--TTI UEs N_(RB) ^(DL) Subband Size k (RBs) M 6-7NA NA  8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

It is also possible to have “M” change based on the subband size and theallocated sBW while the subband size is fixed, which may be only afunction of total system BW or maximum allowable sTTI BW and sTTIlength, as sBW changes.

An sPDCCH can trigger an aperiodic CSI report, such as over the systemBW allocated to sTTI operation. In some cases, an eNB may want to get anaperiodic CSI report from a UE for both 1 ms TTI and sTTI, or possiblyfor two or more different TTI lengths. The reports can be sent indifferent times. For example, an sTTI CSI report can be sent in an sTTIin UL, while a 1 ms-TTI CSI report can be sent later in a 1-ms subframein UL. One solution can be for the eNB to send an (E)PDCCH command totrigger an aperiodic report for 1-ms operation and an sPDCCH command totrigger an aperiodic report for sTTI operation, such as in the samesubframe.

FIG. 11 is an example illustration 1100 of a PDCCH command triggeringaperiodic CSI report for both sTTI and regular TTI, such as 1 ms-TTI,according to a possible embodiment. Another solution for sending CSIreports in different times can enable a eNB to use one control command,such as (E)PDCCH or a special sPDCCH possibly at the beginning of asubframe or in any sTTI in a subframe, to trigger both aperiodic reportspossibly in different time instances. For instance, the sTTI CSI reportcan be sent in an sTTI in UL, while 1 ms-TTI CSI report can be sentlater in a 1-ms subframe in UL. Similar bit-fields used in currentspecifications for triggering an aperiodic report for differentCSI-processes, serving cells, etc. as tabulated in tables 7.2.1.A to7.2.1.E of TS 36.213 can be used to trigger one of the following examplecases: 1 ms-TTI CSI report+sTTI CSI report; 1 ms-TTI CSI report; andsTTI CSI report. The triggered CSI reports may belong to differenttransmission modes, UE-specific RS configurations, CQI bands, etc.corresponding to the different TTI lengths.

A UE can be configured to operate in 1-ms TTI and sTTI, such as 2symbol-TTI (2sym-TTI) and/or 0.5 ms-TTI. Transmission Mode (TM)configuration can be done via higher layers. The UE may be configured tooperate in more than one TTI length, such as 1-ms TTI and 2sym-TTI.There are various ways to configure TMs for multiple TTI length.

One way to configure TMs for multiple TTI length can use independent TMconfigurations. For each TTI length configured for the UE, there can bea separate TM configuration, which can be set along with configurationof the TTI length. For example, a UE can be configured to operate with 1ms-TTI, for which it is RRC configured to do TM-10 with the firstcodebook subset restriction for PMI/RI. Later, the UE can additionallybe configured to operate with 2sym-TTI to do TM-9 with another codebooksubset restriction for PMI/RI. If the UE is scheduled via(E)PDCCH/sPDCCH to send aperiodic CSI for a TTI, it can use thecorresponding parameters, such as codebook subset restriction, of thatTTI.

Another way to way to configure TMs for multiple TTI length can usejoint TM configuration: for all (some) configured TTI lengths, the sameTM configuration can be used. If the same TM is configured for a UE foroperation in 1 ms-TTI and sTTI, some of the configuration parameters canbe different. For instance, the eNB can configure different codebooksubset restriction for different TTI length and/or use the sameconfigured codebook subset restriction as of 1 ms-TTI but withadditional RI restriction. For MAC-CE/Physical control signaling toupdate some TM parameters, as the eNB may have the knowledge of whetherone or multiple TTI lengths are going to be used in near future, it canupdate some parameters of the TM configuration, such as from the defaultparameters indicated in RRC to tailor it to the use-case. For instance,the eNB can communicate with a UE only with 2sym-TTI at least for theduration of the next “X” ms. “X” can be fixed or configured or(semi)dynamically signaled, such as by MAC-CE or physical layer controlcommand.

FIG. 12 is an example flowchart 1200 illustrating the operation of awireless communication device, such as the device 110, according to apossible embodiment. At 1210, a CSI request can be received. The CSIrequest can be received in a control channel. The CSI request canrequest the device to feedback CSI, which can include CQI, PMI, and/orRI.

At 1220, a determination can be made as to whether the CSI requestcorresponds to regular latency based operation or reduced latency basedoperation. The regular latency based operation can be based on a firstcommunication processing time. The reduced latency based operation canbe based on a second communication processing time shorter than thefirst communication processing time. A shorter communication processingtime can be minimum timing reduced compared to that of legacy LTE, suchas 4G, operation, such as for the first TTI lengths. A communicationprocessing time can be a processing time between reception of the ULgrant and the corresponding UL transmission. Another example can includetime between reception of DL data and transmission of a correspondingHARQ ACK.

The regular latency based operation can be based on a first TTI lengththat can be based on a first number of OFDM symbols. The reduced latencybased operation can be based on at least a second TTI length that can bebased on a second number of OFDM symbols. The second number of OFDMsymbols can be shorter than the first number of OFDM symbols. Forexample, the first TTI length can be or can be related to a first numberof OFDM symbols and the second TTI length can be or can be related to asecond number of OFDM symbols. As a further example, the first TTIlength can have a duration of a 1 ms subframe and the second TTI lengthcan be less than the duration of the 1 ms subframe. The term “subframe”can refer to a time domain container spanning a fixed number of OFDMsymbols. The term “subframe” can also be used for describing somethingmore, such as a particular set of signals/channels present within acontainer. For example, ‘subframe duration’ can be 1 ms for a numerologywith 15 kHz subcarrier spacing, and ½m ms for numerology with 2 m*15 kHzsubcarrier spacing. A subframe can include a fixed number of 14 OFDMsymbols.

According to a possible implementation, the CSI request can be receivedin a subframe. The second TTI length can be a duration within thesubframe shorter than the length of the subframe. The CSI request cancorrespond to a regular latency based operation when the CSI request isreceived in a control channel in at least a first symbol of thesubframe. The CSI request can correspond to reduced latency basedoperation when the CSI request is received in a control channel receivedin a TTI with the second TTI length within the subframe.

The CSI request can be determined to correspond to regular latency basedoperation or reduced latency based operation based on an indicatorincluded in the control channel. For example, the control channel caninclude an indicator that indicates a CSI request and can include anindicator that indicates the type of latency based operation. Theindicator that indicates the type of latency can also be included in theCSI request in the control channel. The indicator can be specific bits,can be a CRC mask, or can be any other indicator.

At 1230, CSI can be derived based on a first reference resource when theCSI request corresponds to regular latency based operation. A referenceresource can be a set of time frequency resources assumed by the UE andused for computation of a CQI index corresponding to a MCS value suchthat a transport block can be transmitted over the reference resourcewith the MCS value within a certain BLER, such as not exceeding 0.1.

At 1240, CSI can be derived based on a second reference resource whenthe CSI request corresponds to reduced latency based operation. Thereduced latency based operation can have a latency less than the regularlatency based operation.

Deriving CSI based on the second reference resource can include derivingCSI based on a first subband size when the CSI request corresponds toreduced latency based operation. The first subband size can bedetermined based on a number of resource blocks used for reduced latencybased operation. A subband can be a set of a number of contiguousphysical resource blocks. According to this implementation, deriving CSIbased on a first reference resource in block 1230 can include derivingCSI based on a second subband size when the CSI request corresponds toregular latency based operation. The second subband size can bedetermined based on a number of resource blocks used for regular latencybased operation. The second subband size can also be determined based onsystem bandwidth, such as in legacy LTE, or other factors. The firstsubband size can be greater than the second subband size to possiblyreduce the feedback overhead for sTTI operation or to align subband sizewith resource allocation size in terms of number of RBs. For example,subband size can be a fraction of the resource allocation size.

According to a possible embodiment, deriving CSI based on the firstreference resource can also include deriving CSI based on a restrictionto a first subset of precoders belonging to a set of precoders. DerivingCSI based on the second reference resource can include deriving CSIbased on a restriction to a second subset of precoders belonging to theset of precoders. The second subset of precoders can be different fromthe first subset of precoders. The first subset of precoders can overlapthe second subset of precoders while including at least one differentprecoder or the first subset of precoders can be mutually exclusive fromthe second subset of precoders.

According to another possible embodiment, deriving CSI based on thesecond reference resource can include deriving CSI based on arestriction to a RI value associated with the CSI. Rank can be a numberof simultaneous spatial streams possible for communication between abase station and device. For example, if the base station has eightantennas and the device has four antennas, up to four spatial streamscan be possible. When channel conditions are not good, fewer than fourspatial streams can be possible. “Codebook subset restriction” in theLTE specifications can refer to an indication restricting the number ofprecoders corresponding to a particular rank from a set of precoders forthat rank. As discussed in the present disclosure for joint TMconfiguration, for all or some configured TTI lengths, the same TMconfiguration can be used. If the same TM is configured for a UE foroperation in 1 ms-TTI and sTTI, some of the configuration parameters canbe different. For instance, the base station can use the same configuredcodebook subset restriction as of 1 ms-TTI, but with an additional RIrestriction. The base station and UE can have the same assumption withrespect to codebook subset restriction. As also discussed in the presentdisclosure, the sCSI may not include sRI, and for rank information, thebase station may rely on the most recent RI reported, such as for 1 msoperation, for the purpose of sTTI scheduling, which can be subject to apossible rank restriction. For example, ranks higher than 4 may not bepossible in an sTTI for sTTI operation, whereas ranks up to 8 can bepossible for a subframe for 1 ms operation. As a further example,according to Technical Specification (TS) 36.213, “A UE is restricted toreport PMI, RI and PTI within a precoder codebook subset specified byone or more bitmap parameter(s) codebookSubsetRestriction,codebookSubsetRestriction-1, codebookSubsetRestriction-2,codebookSubsetRestriction-3 configured by higher layer signaling . . . .For a specific precoder codebook and associated transmission mode, thebitmap can specify all possible precoder codebook subsets from which theUE can assume the eNB may be using when the UE is configured in therelevant transmission mode.”

According to another possible embodiment, deriving the CSI based on thesecond reference resource can include deriving CSI based on a RIassumption corresponding to the regular latency operation. For example,the restriction to the RI value associated with the CSI can bedetermined according to a RI assumption corresponding to the regularlatency operation. As discussed above, the rank of the channel may notchange between regular TTI and sTTI operation. Thus, in some examples,the UE may assume for sTTI CSI computation the rank is same as the rankof the most recent RI reported for regular TTI. This can help withreducing the sTTI CSI computation complexity. The regular TTI and sTTICSI configurations can be in the same CSI process. In other embodiments,the UE can be explicitly configured with a ‘RI-reference’ regular TTICSI process to use for sTTI operation, such as a sTTI CSI process. Thiscan be for the case when regular TTI and sTTI CSI are independentlyconfigured in different CSI processes. The set of restricted RIs withprecoder codebook subset restriction can be the same for sTTI andregular TTI CSI. The CSI reporting mode can support RI reporting forregular TTI CSI.

At 1250, the derived CSI can be reported to a network. For example, theCSI can be transmitted to a base station, sent to an access point, orotherwise reported to a network.

FIG. 13 is an example flowchart 1300 illustrating the operation of awireless communication device, such as the device 110, according to apossible embodiment. At 1310, an indication can be received at thedevice from a network. The indication can request the device to feedbackCSI corresponding to a first TTI length operation and/or a second TTIlength operation. The indication can request the device to feedback CSIcorresponding to a first TTI length operation in a control channelassociated with the first TTI length operation and/or a second TTIlength operation in a control channel associated with the second TTIlength operation.

The indication can be received in an explicit CSI request on a controlchannel. The indication can also be implicit. For example, an implicitindication can occur whenever the device, such as a UE, receives asPDSCH corresponding to sTTI operation or receives a resource assignmentassigning resources with sTTI granularity. The UE can feedback CSI forthe sTTI operation. Such implicit CSI feedback behavior can be, forexample, configured by higher layers, can be associated using a separateidentifier, such as RNTI, can be DCI format for the DL control channelscarrying sTTI based resource assignments, and/or can be otherwiseimplicit CSI feedback behavior. Another implicit CSI request can be aperiodic CSI report in which CSI can be reported periodically with acertain interval specified by higher layer message, such as RRCConnection Reconfiguration, RRC Connection Setup, or other higher layermessage. The indication can also be received in a RACH Response (RAR)message instead of a control channel.

The indication can be provided by a layer higher than physical layersignaling. For example, a CSI request can be implicit by being aperiodic CSI report in which CSI can be reported periodically. Theindication can request CSI feedback to be reported in a plurality oftime instances. The time instances in the plurality of time instancescan be equidistant in time.

At 1320, a determination can be made as to whether the CSI indicationrequests CSI feedback for the first TTI length operation and/or thesecond TTI length operation. The first TTI length operation can have ashorter time duration than the second TTI length operation and/or canhave a same time duration as the second TTI length operation, but can beassociated with a shorter communication processing time than acommunication processing time associated with the second TTI operation.

The CSI feedback indication can be determined to be for the first TTIlength operation based on a first RNTI. The CSI feedback indication canbe determined to be for the second TTI length operation based on asecond RNTI.

The determination can be based on a control field corresponding to theindication. The control field can be received in control signaling froma network. For example, the control field can be received in DCI on acontrol channel, such as on the PDCCH or the sPDCCH or can be receivedin a RAR grant. The DCI can also be received in a RAR grant. The RARgrant can be received in a PDSCH. The PDSCH assignment can be providedin a DCI on a control channel, such as PDCCH, with CRC scrambled withRA-RNTI.

The CSI feedback indication can be for the second TTI length operationand can be received in a TTI within a subframe, and the TTI within thesubframe is of the first TTI length. The reference signals associatedwith the second reference TTI can include reference signals transmitteduntil the end of the second reference TTI. A first OFDM symbol of thesecond TTI may not coincide with a first OFDM symbol of the subframe.

At 1330, a first reference TTI of a first TTI length can be determinedbased on the TTI in which the indication is received when the indicationrequests CSI feedback for the first TTI length operation. In differentsteps of the flowchart 1300, a reference TTI may be before, on, or afterthe TTI in which the indication is received.

At 1340, a channel measurement to compute the CSI can be derived usingreference signals associated with the first reference TTI. Alternatelyor in addition to deriving the channel measurement, an interferencemeasurement to compute the CSI can be derived using measurements made onresource elements associated with the first reference TTI.

At 1350, a second reference TTI of a second TTI length can be determinedbased on the TTI in which the indication is received when the indicationrequests CSI feedback for the second TTI length operation. The firstreference TTI can include a first set of frequency resources and thesecond reference TTI can include a second set of frequency resources.The first set and the second set of frequency resources can bedifferent. The first and second set of frequency resources may notnecessarily be different in all instances. The sets of frequencyresources can be sets of time-frequency resources. The first set offrequency resources and/or the second set of frequency resources can bedetermined based on system bandwidth split between the first TTI lengthoperation and the second TTI length operation.

At 1360, the channel measurement to compute the CSI can be derived usingreference signals associated with the second reference TTI. Alternatelyor in addition to determining the channel measurement, an interferencemeasurement to compute the CSI can be determined using measurements madeon resource elements associated with the second reference TTI. At 1370,a first CQI index can be derived and reported based on the firstreference TTI and/or a second CQI index can be derived and reportedbased on the second reference TTI. The first CQI index can be reportedas an offset to the most recently reported second CQI index.

For example, a wideband CQI for sTTI operation can be encodeddifferentially, such as by using 1 or 2-bits, with respect to mostrecent wideband CQI reported for regular TTI operation to help withreducing the feedback overhead. This can be used when CSI for bothregular TTI and sTTI are reported at the same time. For example,wideband differential CQI sTTI offset level=sTTI wideband CQIindex−regular TTI wideband CQI index, as discussed in embodiments above.

Deriving and reporting can include deriving and reporting the first CQIindex based on the first reference TTI, the second CQI index based onthe second reference TTI, and/or a third CQI index along with the firstCQI index. The first CQI index can be derived based on a first overheadassumption associated with the first TTI reference. The third CQI indexcan be derived based on a second overhead assumption associated with thefirst TTI reference. Overhead can include resource elements reserved forcontrol signals and pilot signals. Also, an overhead assumption caninclude at least one selected from a number of PDCCH symbols, and anumber of Cell specific Reference Signal Resource Elements (CRS-REs).Overhead assumption can assume a certain number of resource elements areused for overhead. When deriving a CQI index based on an overheadassumption associated with a TTI reference, the overhead associated withthe TTI reference can be used for CQI derivation regardless of whetherthe used overhead is correct.

FIG. 14 is an example flowchart 1400 illustrating the operation of awireless communication device, such as the base station 120, accordingto a possible embodiment. At 1410, control signaling containing a CSIrequest can be transmitted to a device, such as the device 110.Transmitting can be performed by use of a controller, such as aprocessor, and a transceiver. The CSI request can request the device tofeedback channel state information corresponding to a first TTI lengthoperation and/or a second TTI length operation. The first TTI lengthoperation can have a different TTI length than the second TTI lengthoperation. The CSI request can request the device to feedback CSIcorresponding to a first TTI length operation in a control channelassociated with the first TTI length operation. The CSI request can alsorequest the device to feedback CSI corresponding to a second TTI lengthoperation in a control channel associated with the second TTI lengthoperation.

The CSI request can be provided by a layer higher than physical layersignaling. The CSI request can request CSI feedback to be reported in aplurality of time instances. For example, a CSI request can be implicitby being a periodic CSI report in which CSI can be reportedperiodically. The time instances in the plurality of time instances canbe equidistant in time.

At 1420, a set of time-frequency resources can be scheduled for thedevice to transmit the requested CSI. The set of time-frequencyresources to transmit the requested CSI can be scheduled by allocatingthe set of time-frequency resources to the device. The set oftime-frequency resources include a first set of time-frequency resourcesand a second set of time-frequency resources. The first set oftime-frequency resources can belong to a first TTI of the first length.The second set of time-frequency resources can belong to a second TTI ofthe second length. The first and second set may not necessarily bedifferent in all instances. The first TTI can occur before the secondTTI in time. For example, the first TTI can occur in an earlier ULsubframe than the second TTI. The first set of time-frequency resourcesand/or the second set of time-frequency resources can be determined atleast based on system bandwidth split between the first TTI lengthoperation and the second TTI length operation. At 1430, the CSI can bereceived in the scheduled set of time-frequency resources.

FIG. 15 is an example flowchart 1500 illustrating the operation of awireless communication device, such as the device 110, according to apossible embodiment. At 1510, a configuration can be received. Theconfiguration can configure a plurality of control decoding candidates.

At 1520, a first set of the plurality of control decoding candidatesassociated with a first set of aggregation levels can be monitored in afirst TTI of a subframe. Monitoring can imply attempting to decode. At1530, a second set of the plurality of control decoding candidatesassociated with a second set of aggregation levels can be monitored in asecond TTI of the subframe. The first set of aggregation levels can bedifferent than the second set of aggregation levels. The first andsecond sets of the plurality of control decoding candidates can bedifferent at least in one control decoding candidate. A number ofdecoding candidates in the first set of the plurality of controldecoding candidates can be different from a number of decodingcandidates in the second set of the plurality of control decodingcandidates.

The first TTI and the second TTI can be sTTI, such as a TTI shorterthan, and/or associated with a shorter processing time than another TTIin a subframe. The terms first TTI and second TTI can be used todifferentiate the TTIs from each other and do not necessarily representthe location of the TTIs in the subframe. For example, the first TTI isnot necessarily the first absolute TTI of the subframe and the secondTTI is not necessarily the TTI immediately following the first TTI. Thefirst TTI can be in a first slot of the subframe and the second TTI canbe in a second slot of the subframe.

The first set and second set of the plurality of control decodingcandidates can be based on a UE identifier, a subframe index, an indexassociated with the first TTI within the subframe, an index associatedwith the second TTI within the subframe, and/or any other usefulinformation. The index associated with the first and/or the second TTIwithin the subframe can be a sTTI index within the subframe. A sTTIindex can be associated with a TTI with a length shorter than a lengthof a subframe. The index associated with the first TTI and/or the secondTTI within the subframe can be a slot index corresponding to the firstTTI and/or the second TTI of the subframe.

The second set of the plurality of control decoding candidates can bebased on the first set of the plurality of control decoding candidates.A position of control decoding candidates of the second set of theplurality of control decoding candidates can be derived based onknowledge of positions of control decoding candidates in the first setof the plurality of control decoding candidates. The positions can be inCCEs in the frequency domain.

The first set of the plurality of control decoding candidates can bemapped to a first set of PRB-sets. The second set of the plurality ofcontrol decoding candidates can be mapped to a second set of PRB-sets.The first set of PRB-sets can have at least one different PRB-set fromthe second set of PRB-sets.

A TTI can be a duration in which the device can transmit and receive aTransport Block (TB) to and from higher layers than a physical layer.For example, the term “TTI” can refer to the duration in which thedevice can receive/transmit a TB from higher layers, such as a MAC PDUfrom a MAC layer that is higher than a physical layer. Therefore, theTTI length can depend on how TBs are mapped to REs and OFDM symbols. TheTTI can include resources for a control channel, which can be used forresource assignment within the TTI to the device.

FIG. 16 is an example flowchart 1600 illustrating the operation of awireless communication device, such as the base station 120, accordingto a possible embodiment. At 1610, a plurality of control decodingcandidates can be configured. The plurality of control decodingcandidates can be configured using a controller, such as a processor.

At 1620, a first control signal can be transmitted in a control decodingcandidate belonging to a first set of the plurality of control decodingcandidates associated with a first set of aggregation levels in a firstTTI of a subframe. At 1630, a second control signal can be transmittedin a control decoding candidate belonging to a second set of theplurality of control decoding candidates associated with a second set ofaggregation levels in a second TTI of a subframe. The first and secondsets of the plurality of control decoding candidates can be different atleast in one control decoding candidate. Also, the first set ofaggregation levels can be different than the second set of aggregationlevels.

According to a possible implementation, the first set and second set ofthe plurality of control decoding candidates can be based on a UEidentifier, a subframe index, an index associated with the first TTIwithin the subframe, an index associated with the second TTI within thesubframe, and/or other information. The index associated with the firstTTI and/or the second TTI within the subframe can be a sTTI index withinthe subframe. A sTTI index can be associated with a TTI with a lengthshorter than a length of a subframe. The index associated with at leastone selected from the first TTI and the second TTI within the subframecan be a slot index corresponding to the first TTI and/or the second TTIof the subframe.

According to a possible implementation, the first TTI can be in a firstslot of the subframe and the second TTI can be in a second slot of thesubframe. The number of decoding candidates in the first set and thesecond set of the plurality of control decoding candidates can bedifferent. The second set of the plurality of control decodingcandidates can be based on the first set of the plurality of controldecoding candidates.

According to a possible implementation, the first set of the pluralityof control decoding candidates can be mapped to a first set of PRB-sets.The second set of the plurality of control decoding candidates can bemapped to a second set of PRB-sets. The first set of PRB-sets and thesecond set of PRB-sets can have at least one different PRB-set.

FIG. 17 is an example flowchart 1700 illustrating the operation of awireless communication device, such as the device 110, according to apossible embodiment. At 1710, a determination can be made as to whetherthe device is configured to communicate using a second TTI length in asubframe. The second TTI length can be shorter than a first TTI length.At 1720, a first set of control decoding candidates corresponding to thefirst TTI length in a subframe can be monitored when the device is notconfigured to communicate using the second TTI length in the subframe.Monitoring can imply attempting to decode.

At 1730, a second set of control decoding candidates corresponding tothe first TTI length in the subframe can be monitored if the device isconfigured to communicate using the second TTI length in the subframe.The first and the second sets can be different. A number of candidatesin the second set can be less than a number of candidates in the firstset. The second set can be a proper subset of the first set. The firstTTI length can be a length of a subframe.

At 1740, a third set of control decoding candidates corresponding to thesecond TTI length in at least a first portion of the subframe can bemonitored when the device is configured to communicate using the secondTTI length in the subframe. The first portion of the subframe can beless than the entire length of the subframe. For example, the firstportion of the subframe can be a first number of OFDM symbols in thesubframe less than the total number of OFDM symbols of the subframe.

At 1750, a fourth set of control decoding candidates corresponding tothe second TTI length in at least a second portion of the subframe canbe monitored when the device is configured to communicate using thesecond TTI length in the subframe. The second portion can be differentthan the first portion. For example, the second portion can betemporally separate from the first portion. The number of candidates inthe fourth set of control decoding candidates can be larger than thenumber of candidates in the third set of control decoding candidates.The first portion of the subframe can correspond to a first TTI with alength associated with the second TTI length. The second portion of thesubframe can correspond to a second TTI different from the first TTI.The second TTI can have a length associated with the second TTI length.For example, the second TTI length can be less than a subframe length.The first and second TTIs may or may not have the same length. The firstportion of the subframe can correspond to a first slot of the subframeand the second portion of the subframe can correspond to a second slotof the subframe.

According to a possible implementation, the second set of controldecoding candidates corresponding to the first TTI length in thesubframe can be monitored in the first slot of the subframe. Adifference between the number of candidates in the fourth set and a sumof the number of candidates in the second set and the number ofcandidates in the third set can be at most a non-negative number. Forexample, a sum of the number of candidates in the second set and thenumber of candidates in the third set can be larger than a number ofcandidates in the fourth set. The non-negative number can be equal tothe number of TTIs in the first portion of the subframe or the number ofTTIs in the second portion of the subframe. The sum of the number ofcandidates of the second and third set can be, but is not necessarily,equal to the number of candidates in the fourth set.

It should be understood that, notwithstanding the particular steps asshown in the figures, a variety of additional or different steps can beperformed depending upon the embodiment, and one or more of theparticular steps can be rearranged, repeated or eliminated entirelydepending upon the embodiment. Also, some of the steps performed can berepeated on an ongoing or continuous basis simultaneously while othersteps are performed. Furthermore, different steps can be performed bydifferent elements or in a single element of the disclosed embodiments.

FIG. 18 is an example block diagram of an apparatus 1800, such as the UE110, the base station 120, or any other wireless communication devicedisclosed herein, according to a possible embodiment. The apparatus 1800can include a housing 1810, a controller 1820 coupled to the housing1810, audio input and output circuitry 1830 coupled to the controller1820, a display 1840 coupled to the controller 1820, a transceiver 1850coupled to the controller 1820, an antenna 1855 coupled to thetransceiver 1850, a user interface 1860 coupled to the controller 1820,a memory 1870 coupled to the controller 1820, and a network interface1880 coupled to the controller 1820. The apparatus 1800 does notnecessarily include all of the illustrated elements for differentembodiments of the present disclosure. The apparatus 1800 can performthe methods described in all the embodiments.

The display 1840 can be a viewfinder, a Liquid Crystal Display (LCD), aLight Emitting Diode (LED) display, an Organic Light Emitting Diode(OLED) display, a plasma display, a projection display, a touch screen,or any other device that displays information. The transceiver 1850 caninclude a transmitter and/or a receiver. The audio input and outputcircuitry 1830 can include a microphone, a speaker, a transducer, or anyother audio input and output circuitry. The user interface 1860 caninclude a keypad, a keyboard, buttons, a touch pad, a joystick, a touchscreen display, another additional display, or any other device usefulfor providing an interface between a user and an electronic device. Thenetwork interface 1880 can be a Universal Serial Bus (USB) port, anEthernet port, an infrared transmitter/receiver, an IEEE 1394 port, aWLAN transceiver, or any other interface that can connect an apparatusto a network, device, or computer and that can transmit and receive datacommunication signals. The memory 1870 can include a random accessmemory, a read only memory, an optical memory, a solid state memory, aflash memory, a removable memory, a hard drive, a cache, or any othermemory that can be coupled to an apparatus.

The apparatus 1800 or the controller 1820 may implement any operatingsystem, such as Microsoft Windows®, UNIX®, or LINUX®, Android™, or anyother operating system. Apparatus operation software may be written inany programming language, such as C, C++, Java or Visual Basic, forexample. Apparatus software may also run on an application framework,such as, for example, a Java® framework, a .NET® framework, or any otherapplication framework. The software and/or the operating system may bestored in the memory 1870 or elsewhere on the apparatus 1800. Theapparatus 1800 or the controller 1820 may also use hardware to implementdisclosed operations. For example, the controller 1820 may be anyprogrammable processor. Disclosed embodiments may also be implemented ona general-purpose or a special purpose computer, a programmedmicroprocessor or microprocessor, peripheral integrated circuitelements, an application-specific integrated circuit or other integratedcircuits, hardware/electronic logic circuits, such as a discrete elementcircuit, a programmable logic device, such as a programmable logicarray, field programmable gate-array, or the like. In general, thecontroller 1820 may be any controller or processor device or devicescapable of operating an apparatus and implementing the disclosedembodiments. Some or all of the additional elements of the apparatus1800 can also perform some or all of the operations of the disclosedembodiments.

According to a possible embodiment, the transceiver 1850 can receive aCSI request requesting the apparatus 1800 to feedback channel stateinformation. The controller 1820 can determine whether the CSI requestcorresponds to regular latency based operation or reduced latency basedoperation. The controller 1820 can derive CSI based on a first referenceresource when the CSI request corresponds to regular latency basedoperation. The controller 1820 can derive CSI based on a secondreference resource when the CSI request corresponds to reduced latencybased operation. The reduced latency based operation can have a latencyless than the regular latency based operation. The controller 1820 canreport the derived CSI to a network.

The regular latency based operation can be based on a firstcommunication processing time. The reduced latency based operation canbe based on a second communication processing time shorter than thefirst communication processing time. A regular latency based operationcan be based on a first TTI length based on a first number of OFDMsymbols. A reduced latency based operation can be based on at least asecond TTI length based on a second number of OFDM symbols. The secondnumber of OFDM symbols can be shorter than the first number of OFDMsymbols.

According to a possible implementation, the CSI request can be receivedin a subframe. The second TTI length can be a duration within thesubframe shorter than the length of the subframe. The CSI request cancorresponds to a regular latency based operation when the CSI request isreceived in a control channel in at least a first symbol of thesubframe. The CSI request can correspond to reduced latency basedoperation when the CSI request is received in a control channel receivedin a TTI with the second TTI length within the subframe.

According to a possible implementation, the CSI request can be receivedin a control channel. The controller 1820 can determine whether the CSIrequest corresponds to regular latency based operation or reducedlatency based operation based on an indicator included in the controlchannel.

According to a possible implementation, the controller 1820 can deriveCSI based on the second reference resource by deriving CSI based on afirst subband size when the CSI request corresponds to reduced latencybased operation. The first subband size can be determined based on anumber of resource blocks used for reduced latency based operation.

According to a possible implementation, the controller 1820 can deriveCSI based on a first reference resource by deriving CSI based on asecond subband size when the CSI request corresponds to regular latencybased operation. The second subband size can be determined based on anumber of resource blocks used for regular latency based operation.

According to a possible implementation, the controller 1820 can derivedCSI based on the first reference resource by deriving CSI based on arestriction to a first subset of precoders belonging to a set ofprecoders. The controller 1820 can derive CSI based on the secondreference resource by deriving CSI based on a restriction to a secondsubset of precoders belonging to the set of precoders. The second subsetof precoders can be different from the first subset of precoders.

According to other possible implementations, the controller 1820 canderive CSI based on the second reference resource by deriving CSI basedon a restriction to a RI value associated with the CSI. The controller1820 can also derive the CSI based on the second reference resource byderiving CSI based on a RI assumption corresponding to the regularlatency operation.

According to another possible embodiment, the controller 1820 cancontrol operations of the apparatus 1800. The transceiver 1850 canreceive an indication from a network. The indication can request thedevice to feedback CSI corresponding to a first TTI length operationand/or a second TTI length operation.

When the indication requests CSI feedback for the first TTI lengthoperation, the controller 1820 can determine a first reference TTI of afirst TTI length based on the TTI in which the indication is received.The controller 1820 can also derive a channel measurement to compute theCSI using reference signals associated with the first reference TTIand/or can derive an interference measurement to compute the CSI usingmeasurements made on resource elements associated with the firstreference TTI.

When the indication requests CSI feedback for the second TTI lengthoperation, the controller 1820 can determine a second reference TTI of asecond TTI length based on the TTI in which the indication is received.The controller 1820 can also derive the channel measurement to computethe CSI using reference signals associated with the second reference TTIand/or can derive the interference measurement to compute the CSI usingmeasurements made on resource elements associated with the secondreference TTI.

The first TTI length operation can have a shorter time duration than thesecond TTI length operation and/or can have a same time duration as thesecond TTI length operation but can be associated with a shortercommunication processing time than a communication processing timeassociated with the second TTI operation.

According to a possible implementation, the first reference TTI caninclude a first set of frequency resources. The second reference TTI caninclude a second set of frequency resources. The first set and thesecond set can be different. According to another possibleimplementation, the first set of frequency resources and/or the secondset of frequency resources can be determined at least based on systembandwidth split between the first TTI length operation and the secondTTI length operation.

According to another possible implementation, the controller 1820 canderive and report a first CQI index based on the first reference TTIand/or a second CQI index based on the second reference TTI. The firstCQI index can be reported as an offset to the most recently reportedsecond CQI index. The controller 1820 can derive and report the firstCQI index based on the first reference TTI, the second CQI index basedon the second reference TTI, and/or a third CQI index along with thefirst CQI index. The first CQI index can be derived based on a firstoverhead assumption associated with the first TTI reference. The thirdCQI index can be derived based on a second overhead assumptionassociated with the first TTI reference. An overhead assumption caninclude a number of PDCCH symbols and/or a number of CRS resourceelements.

According to another possible embodiment, the transceiver 1850 cantransmit control signaling containing a CSI request to a device. The CSIrequest can request the device to feedback channel state informationcorresponding to a first TTI length operation and/or a second TTI lengthoperation. The CSI request can request the device to feedback CSIcorresponding to a first TTI length operation in a control channelassociated with the first TTI length operation and/or a second TTIlength operation in a control channel associated with the second TTIlength operation. The CSI request can be provided by a layer higher thanphysical layer signaling. The CSI request can request CSI feedback to bereported in a plurality of time instances. The time instances in theplurality of time instances can be equidistant in time.

The controller 1820 can schedule a set of time-frequency resources forthe device to transmit the requested CSI. The transceiver 1850 canreceive the CSI in the scheduled set of time-frequency resources.

According to a possible implementation, the set of time-frequencyresources can include a first set of time-frequency resources and asecond set of time-frequency resources. The first set of time-frequencyresources can belong to a first TTI of the first length. The second setof time-frequency resources can belong to a second TTI of the secondlength.

The first TTI can occur before the second TTI in time. The first set oftime-frequency resources and/or the second set of time-frequencyresources can be determined at least based on system bandwidth splitbetween the first TTI length operation and the second TTI lengthoperation.

According to another possible embodiment, the transceiver 1850 canreceive a configuration that configures a plurality of control decodingcandidates. The controller 1820 can monitor a first set of the pluralityof control decoding candidates associated with a first set ofaggregation levels in a first TTI of a subframe. The controller 1820 canmonitor a second set of the plurality of control decoding candidatesassociated with a second set of aggregation levels in a second TTI ofthe subframe. The first and second sets of the plurality of controldecoding candidates can be different at least in one control decodingcandidate. The first set of aggregation levels can be different than thesecond set of aggregation levels. A TTI can be a duration in which theapparatus 1800 can transmit and receive a transport block to and fromhigher layers than a physical layer.

According to a possible implementation, the first set and second set ofthe plurality of control decoding candidates can be based on a UEidentifier, a subframe index, an index associated with the first TTIwithin the subframe, and/or an index associated with the second TTIwithin the subframe. The index associated with the first and/or thesecond TTI within the subframe can be a sTTI index within the subframe.The sTTI index can be associated with a TTI with a length shorter than alength of a subframe. The index associated with the first TTI and/or thesecond TTI within the subframe can be a slot index corresponding to thefirst TTI and/or the second TTI of the subframe.

According to another possible implementation, first TTI can be in afirst slot of the subframe and the second TTI can be in a second slot ofthe subframe. According to another possible implementation, a number ofdecoding candidates in the first set and the second set of the pluralityof control decoding candidates can be different.

According to another possible implementation, second set of theplurality of control decoding candidates can be based on the first setof the plurality of control decoding candidates. The controller 1820 canderive a position of control decoding candidates of the second set ofthe plurality of control decoding candidates based on knowledge ofpositions of control decoding candidates in the first set of theplurality of control decoding candidates.

According to another possible implementation, the first set of theplurality of control decoding candidates can be mapped to a first set ofPRB-sets. The second set of the plurality of control decoding candidatescan be mapped to a second set of PRB-sets. The first set of PRB-sets andthe second set of PRB-sets can have at least one different PRB-set.

According to a possible embodiment, the controller 1820 can configure aplurality of control decoding candidates. The transceiver 1850 cantransmit a first control signal in a control decoding candidatebelonging to a first set of the plurality of control decoding candidatesassociated with a first set of aggregation levels in a first TTI of asubframe. The transceiver 1850 can transmit a second control signal in acontrol decoding candidate belonging to a second set of the plurality ofcontrol decoding candidates associated with a second set of aggregationlevels in a second TTI of a subframe. The first and second sets of theplurality of control decoding candidates can be different at least inone control decoding candidate. The first set of aggregation levels canbe different than the second set of aggregation levels. The first TTIcan be in a first slot of the subframe and the second TTI is in a secondslot of the subframe. The number of decoding candidates in the first setand the second set of the plurality of control decoding candidates canbe different. The second set of the plurality of control decodingcandidates can be based on the first set of the plurality of controldecoding candidates.

According to a possible implementation, the first set and second set ofthe plurality of control decoding candidates can be based on a UEidentifier, a subframe index, an index associated with the first TTIwithin the subframe, and/or an index associated with the second TTIwithin the subframe. The index associated with the first and/or thesecond TTI within the subframe can be a sTTI index within the subframe.A sTTI index can be associated with a TTI with a length shorter than alength of a subframe. The index associated with the first TTI and/or thesecond TTI within the subframe can be a slot index corresponding to thefirst TTI and/or the second TTI of the subframe.

According to a possible implementation, the first set of the pluralityof control decoding candidates can be mapped to a first set of PRB-sets.The second set of the plurality of control decoding candidates can bemapped to a second set of PRB-sets. The first set of PRB-sets and thesecond set of PRB-sets can have at least one different PRB-set.

According to a possible embodiment, the transceiver 1850 can transmitand receive signals in subframes over a wireless network. The controller1820 can monitor a first set of control decoding candidatescorresponding to a first TTI length in a subframe when the apparatus1800 is not configured to communicate using a second TTI length in thesubframe. The second TTI length can be shorter than the first TTIlength.

The controller 1820 can monitor a second set of control decodingcandidates corresponding to the first TTI length in the subframe whenthe apparatus 1800 is configured to communicate using the second TTIlength in the subframe. The first and the second sets can be differentand the number of candidates in the second set is less than the numberof candidates in the first set.

The controller 1820 can monitor a third set of control decodingcandidates corresponding to the second TTI length in at least a firstportion of the subframe when the apparatus 1800 is configured tocommunicate using the second TTI length in the subframe. A length of thefirst portion of the subframe can be less than the entire length of thesubframe.

The controller 1820 can monitor a fourth set of control decodingcandidates corresponding to the second TTI length in at least a secondportion of the subframe when the apparatus 1800 is configured tocommunicate using the second TTI length in the subframe. The secondportion can be different than the first portion.

According to a possible implementation, the number of candidates in thefourth set of control decoding candidates can be larger than the numberof candidates in the third set of control decoding candidates. Accordingto a possible implementation, the first portion of the subframe cancorrespond to a first TTI with a length associated with the second TTIlength. According to a possible implementation, the second portion ofthe subframe corresponds to a second TTI different from the first TTI.The second TTI can have a length associated with the second TTI length.According to a possible implementation, the first portion of thesubframe can correspond to a first slot of the subframe and the secondportion of the subframe can correspond to a second slot of the subframe.

According to a possible implementation, the second set of controldecoding candidates corresponding to the first TTI length in thesubframe can be monitored in the first slot of the subframe. Adifference between the number of candidates in the fourth set and a sumof the number of candidates in the second set and the number ofcandidates in the third set can be at most a non-negative number. Thenon-negative number can be equal to the number of TTIs in the firstportion of the subframe or the number of TTIs in the second portion ofthe subframe.

The method of this disclosure can be implemented on a programmedprocessor. However, the controllers, flowcharts, and modules may also beimplemented on a general purpose or special purpose computer, aprogrammed microprocessor or microcontroller and peripheral integratedcircuit elements, an integrated circuit, a hardware electronic or logiccircuit such as a discrete element circuit, a programmable logic device,or the like. In general, any device on which resides a finite statemachine capable of implementing the flowcharts shown in the figures maybe used to implement the processor functions of this disclosure.

While this disclosure has been described with specific embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art. For example,various components of the embodiments may be interchanged, added, orsubstituted in the other embodiments. Also, all of the elements of eachfigure are not necessary for operation of the disclosed embodiments. Forexample, one of ordinary skill in the art of the disclosed embodimentswould be enabled to make and use the teachings of the disclosure bysimply employing the elements of the independent claims. Accordingly,embodiments of the disclosure as set forth herein are intended to beillustrative, not limiting. Various changes may be made withoutdeparting from the spirit and scope of the disclosure.

In this document, descriptions may be given relating embodiments toimplementation within standardized operations of devices, which mayrequire the devices to operate in specified manners. Thus, terms such as“shall,” “is,” and other similar terminology is used to suggeststandardized operations of devices. However, such terms do not limit theembodiments in the sense that standardized operations may change,embodiments may operate in different contexts outside of standardizedguidelines, embodiments may operate in different contexts according todifferent standardized guidelines, and other operations and elements arepossible unless specifically required in the claims.

Furthermore, relational terms such as “first,” “second,” and the likemay be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. The phrase“at least one of,” “at least one selected from the group of,” or “atleast one selected from” followed by a list is defined to mean one,some, or all, but not necessarily all of, the elements in the list. Theterms “comprises,” “comprising,” “including,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus. An element proceeded by “a,” “an,” or the like does not,without more constraints, preclude the existence of additional identicalelements in the process, method, article, or apparatus that comprisesthe element. Also, the term “another” is defined as at least a second ormore. The terms “including,” “having,” and the like, as used herein, aredefined as “comprising.” Furthermore, the background section is writtenas the inventor's own understanding of the context of some embodimentsat the time of filing and includes the inventor's own recognition of anyproblems with existing technologies and/or problems experienced in theinventor's own work.

We claim:
 1. A method performed by a device, the method comprising:receiving an indication from a network, the indication requesting thedevice to feedback channel state information corresponding to at leastone selected from a first transmit time interval length operation and asecond transmit time interval length operation; when the indicationrequests channel state information feedback for the first transmit timeinterval length operation: determining a first reference transmit timeinterval of a first transmit time interval length based on the transmittime interval in which the indication is received; and deriving at leastone selected from a channel measurement to compute the channel stateinformation using reference signals associated with the first referencetransmit time interval, and an interference measurement to compute thechannel state information using measurements made on resource elementsassociated with the first reference transmit time interval; and when theindication requests channel state information feedback for the secondtransmit time interval length operation: determining a second referencetransmit time interval of a second transmit time interval length basedon the transmit time interval in which the indication is received; andderiving at least one selected from a channel measurement to compute thechannel state information using reference signals associated with thesecond reference transmit time interval, and an interference measurementto compute the channel state information using measurements made onresource elements associated with the second reference transmit timeinterval, wherein the first transmit time interval length operation hasone selected from a shorter time duration than the second transmit timeinterval length operation, or a same time duration as the secondtransmit time interval length operation but is associated with a shortercommunication processing time than a communication processing timeassociated with the second transmit time interval operation.
 2. Themethod according to claim 1, wherein the first reference transmit timeinterval comprises a first set of frequency resources, wherein thesecond reference transmit time interval comprises a second set offrequency resources, and wherein the first set of frequency resourcesand the second set of frequency resources are different.
 3. The methodaccording to claim 2, wherein at least one selected from the first setof frequency resources and the second set of frequency resources isdetermined at least based on system bandwidth split between the firsttransmit time interval length operation and the second transmit timeinterval length operation.
 4. The method according to claim 2, furthercomprising deriving and reporting at least one selected from a firstchannel quality indicator index based on the first reference transmittime interval, and a second channel quality indicator index based on thesecond reference transmit time interval.
 5. The method according toclaim 4, wherein the first channel quality indicator index is reportedas an offset to the most recently reported second channel qualityindicator index.
 6. The method according to claim 4, wherein derivingand reporting comprises deriving and reporting at least one selectedfrom the first channel quality indicator index based on the firstreference transmit time interval, the second channel quality indicatorindex based on the second reference transmit time interval, and a thirdchannel quality indicator index along with the first channel qualityindicator index, and wherein the first channel quality indicator indexis derived based on a first overhead assumption associated with thefirst transmit time interval reference, and wherein the third channelquality indicator index is derived based on a second overhead assumptionassociated with the first transmit time interval reference.
 7. Themethod according to claim 6, wherein an overhead assumption includes atleast one selected from a number of physical downlink control channelsymbols, and a number of cell specific reference signal resourceelements.
 8. The method according to claim 1, wherein the indicationrequests the device to feedback channel state information correspondingto at least one selected from a first transmit time interval lengthoperation in a control channel associated with the first transmit timeinterval length operation, and a second transmit time interval lengthoperation in a control channel associated with the second transmit timeinterval length operation.
 9. The method according to claim 1, furthercomprising determining whether the channel state information feedbackindication is for the first transmit time interval length operation orthe second transmit time interval length operation based on a controlfield corresponding to the indication, where the control field isreceived in control signaling from a network.
 10. The method accordingto claim 9, wherein the channel state information feedback indication isfor the second transmit time interval length operation and is receivedin a transmit time interval within a subframe, and the transmit timeinterval within the subframe is of the first transmit time intervallength, and wherein the reference signals associated with the secondreference transmit time interval include reference signals transmitteduntil the end of the second reference transmit time interval, andwherein a first orthogonal frequency division multiplexing symbol of thesecond transmit time interval does not coincide with a first orthogonalfrequency division multiplexing symbol of the subframe.
 11. The methodaccording to claim 1, further comprising: determining the channel stateinformation feedback indication is for the first transmit time intervallength operation based on a first radio network temporary identifier;and determining the channel state information feedback indication is forthe second transmit time interval length operation based on a secondradio network temporary identifier.
 12. The method according to claim 1,wherein the indication is provided by a layer higher than physical layersignaling, and wherein the indication requests channel state informationfeedback to be reported in a plurality of time instances.
 13. The methodaccording to claim 12, wherein the time instances in the plurality oftime instances are equidistant in time.
 14. An apparatus comprising: acontroller that controls operations of the apparatus; and a transceiverthat receives an indication from a network, the indication requestingthe apparatus to feedback channel state information corresponding to atleast one selected from a first transmit time interval length operationand a second transmit time interval length operation, wherein when theindication requests channel state information feedback for the firsttransmit time interval length operation, the controller determines afirst reference transmit time interval of a first transmit time intervallength based on the transmit time interval in which the indication isreceived, and derives at least one selected from a channel measurementto compute the channel state information using reference signalsassociated with the first reference transmit time interval, and aninterference measurement to compute the channel state information usingmeasurements made on resource elements associated with the firstreference transmit time interval, wherein when the indication requestschannel state information feedback for the second transmit time intervallength operation, the controller determines a second reference transmittime interval of a second transmit time interval length based on thetransmit time interval in which the indication is received, and derivesat least one selected from a channel measurement to compute the channelstate information using reference signals associated with the secondreference transmit time interval, and an interference measurement tocompute the channel state information using measurements made onresource elements associated with the second reference transmit timeinterval, and wherein the first transmit time interval length operationhas one selected from a shorter time duration than the second transmittime interval length operation, or a same time duration as the secondtransmit time interval length operation but is associated with a shortercommunication processing time than a communication processing timeassociated with the second transmit time interval operation.
 15. Theapparatus according to claim 14, wherein the first reference transmittime interval comprises a first set of frequency resources, wherein thesecond reference transmit time interval comprises a second set offrequency resources, and wherein the first set and the second set aredifferent.
 16. The apparatus according to claim 15, wherein at least oneselected from the first set of frequency resources and the second set offrequency resources is determined at least based on system bandwidthsplit between the first transmit time interval length operation and thesecond transmit time interval length operation.
 17. The apparatusaccording to claim 15, the controller can derive and report at least oneselected from a first channel quality indicator index based on the firstreference transmit time interval, and a second channel quality indicatorindex based on the second reference transmit time interval.
 18. Theapparatus according to claim 17, wherein the first channel qualityindicator index is reported as an offset to the most recently reportedsecond channel quality indicator index.
 19. The apparatus according toclaim 17, wherein deriving and reporting comprises deriving andreporting at least one selected from the first channel quality indicatorindex based on the first reference transmit time interval, the secondchannel quality indicator index based on the second reference transmittime interval, and a third channel quality indicator index along withthe first channel quality indicator index, and wherein the first channelquality indicator index is derived based on a first overhead assumptionassociated with the first transmit time interval reference, and whereinthe third channel quality indicator index is derived based on a secondoverhead assumption associated with the first transmit time intervalreference.
 20. The apparatus according to claim 19, wherein an overheadassumption includes at least one selected from a number of physicaldownlink control channel symbols, and a number of cell specificreference signal resource elements.